1. Field of the Invention
This invention relates to a production process for producing a novel pigment generating colors by light interference and light scattering. The weather resistance of the novel pigment can be improved remarkably by the production process according to this invention.
2. Related Art Statement
A pearl mica pigment has been known recently. The pearl mica pigment comprises mica and titanium dioxide layer coated on the surface of the mica, and generates pearl like glossiness by light interference. Various interference colors can be obtained by varying the thickness of the titanium dioxide layer. In addition, Japanese Unexamined Patent Publication (KOKAI) No. 78265/1984 and Japanese Examined Patent Publication (KOKOKU) No. 3345/1985 disclose pigments further comprise chromium compound deposited on the surface of the titanium dioxide layer of the pearl mica pigment, thereby improving the weather resistance of the pigments.
A paint film formed by a paint employing the pearl mica pigment, however, does not offer metallic glossiness, nor is appropriate for a metallic paint film application. Further, when compared with a metallic paint film containing aluminum powders, the paint film comprising the pearl mica pigment exhibits small brightness difference between the brightness viewed at the front with respect to the paint film and the brightness viewed at an oblique angle with respect to the paint film, and thus has problems resulting from the so-called inferior flip-flop characteristic. Accordingly, the inventors of this invention applied a patent for a novel pigment by Japanese Patent Application No. 265795/1987 which has not been published when the application of the present invention is filed. The novel pigment comprises a pearl mica pigment and metal or alloy glossy dots formed on the surface of the pearl mica pigment in a scattered manner, and the metal or alloy glossy dots occupying from 0.05 to 95% of the surfaces of the pearl mica pigment with respect to the total surface area of the pearl mica pigment. A metallic paint film formed by a paint employing the novel pigment offers a glossy feeling resulting from the metal or alloy glossy dots, an interference color resulting from light interference, a scattering color resulting from light reflection and scattering, and a superior flip-flop characteristic.
The inventors of this invention, however, have found that the weather resistance of the novel pigment is not satisfactory enough in the course of the research and development of the novel pigment. For instance, the novel pigment, in which silver is deposited by an electroless plating method on the surfaces of the pearl mica pigment in a scattered manner, usually gives a blue color generation, but sometimes gives intense yellowish color generation due to the fluctuations of the production conditions. When the inventors of this invention conducted an accelerated weather resistance test on a paint film, which was formed by a paint employing such novel pigment, by using a QUV apparatus for 500 hours, the yellowish color generation of the paint film had faded away during the test. The inventors of this invention also found that this phenomenon occurred especially in the novel pigments giving intense yellowish color generation which has the "b" value in Hunter's "Lab" value deviating from -2 in the plus direction, i.e., -2 or more, or from 1 to 2 in .DELTA.b value.